Radio receiving circuit



RADIO RECEIVING CIRCUIT Filed Nov. 16, 1928 HIIPIIU'EIII Patented Feb. 6, 1934 UNITED STATES PATENT? OFFICE.

Application November 16, 1928 7 Serial No. 319,806

12 Claims. (Cl. 25020) This invention relates to the art of electric signalling and is for a receiving circuit for radio communication. The invention constitutes an improvement on the invention covered by my prior Patent No. 1,674,448, dated June 19, 1928. In said patent there is disclosed a radio receiving circuit wherein there is a stage of radio frequency amplification, whose output is impressed on a detector having a balanced input grid circuit of unique arrangement.

This system has been found to possess all of the advantages of a superheterodyne circuit operating with a stage of radiofrequency amplification, both as to signal volume and selectivity, but is found to be far less critical and better adapted to general use.

Both the tuned radiofrequency amplifying circuit and the detector circuit are tuned by a variable capacity. I have found that in a circuit such as disclosed in my said patent, where the elements of the two circuits are co-related for proper operation, the tuning of the stage of tuned radiofrequency amplification broadens as the resonance frequency is increased, which is an inherent property of any stage of tuned radiofrequency amplification while, in the balanced detector circuit, the tuning sharpens as the frequency increases and broadens as the frequency decreases. The two circuits therefore work directly opposite, and one compensates for the other. According to the present invention there is provided means for simultaneously tuning both circuits, whereby the operation of the receiving circuit is materially simplified.

I have also found that the input inductance of the tuned radiofrequency circuit may comprise a directional loop, as suggested in my said patent. This directional loop, which comprises the collector of the input circuit, is, under certain conditions of operation, not sufficiently sensitive to afford satisfactory results, and I have found that this deficiency can be corrected by means of a counterpoise coupled directly to the input of the grid. This increases the sensitivity without increasing the tendency toward self-oscillation or disturbing the neutralization of the circuit.

I have also discovered that where the balanced detector circuit is neutralized in the manner disclosed in my said patent, the usual devices for securing rectification can be omitted, whereby the circuit is simplified and the number of parts reduced. Whereas it has heretofore been considered necessary to use a grid resistance and a grid condenser to secure rectification or to impress a biasing. potential on the grid of the tube,

I have found that rectification will be effected without resorting to either of these means, and

with a decided improvement in signal quality.

The invention may be readily understood by reference to the accompanying drawing, in which so the figure is a diagram of one circuit'embodying my invention.

In the drawing, 2 designates-a three element electron tube in the collector or radio frequency amplifying circuit. The tube has a cathode 3 5 which may be heated from any suitable sourceof current, such as the. battery 4. The tube has an anode or plate electrode 5 which is connected with the positive side of a source of plate voltage 6. Interposed between the anode and the cathode is the input or grid electrode '7. The input electrode or grid is connected to an inductance 8 tuned by a variable condenser 9. The midpoint of the inductance 8 is tapped by a wire 10 which connects to one side of the cathode circuit. The other side of the inductance iscoupled to the plate circuit of the tube through a neutralizing capacity 11. The capacity 11 has a value substantially equal to the internal capacity of the tube. This circuit comprises the usual 0 neutralized circuit wherein regeneration is avoided by a system of reverse-phase feed-back.

I prefer that the inductance 8 comprise a collector, and may conveniently be a directional loop, as disclosed in my said patent. For the purpose of increasing sensitivity of the circuit under certain conditions of operation, I have found that a counterpoise aerial may be effectively used. In the figure there is shown a connection 12 leading to the input or grid circuit. At 13 is a switch through which the conductor 12 may be coupled to the counterpoise 14. In the circuit shown, there is no ground, and none in this circuit is desired.

I have illustrated the switch 13 as having several points 13a, 13b and 130. When the switch is contacting with point 13a, the counterpoise is directly connected to the grid circuit; and when the switch is in contact with point 13b, the counterpoise is capacitively coupled to the grid circuit;. and. when the switch is in contact with point 130, there is an inductive coupling, which may be a loose coupling, as indicated by the radiofrequency transformer 13d. 7

Amplified signal impulses from the output of the tube 2 are impressed on the grid circuit of a detector tube 15, which is also a three electrode tube. As one means of transferring the signal impulses from the plate circuit of thetube ,2 to the grid circuit of the tube 15, I have shown an H0 inductive coupling 16 having a primary winding 1'7 and a secondary winding 18. One end of the i winding 18 is connected through a wire 19 to the midpoint of a grid circuit inductance 20, which is preferably a toroidal coil. One end of the inductance 20 is connected through a wire 21, variable capacity 22 and wire 23 to the ground or cathode return circuit 24. The other end of the inductance 20 is connected through wire 25, fixed capacity 26, and wire 23 to the cathode return circuit. Bridged across the wires 21 and 25 is a variable capacity 27, preferably a straight line frequency condenser of the same value as the condenser 9.

The tube 15 has a cathode 28, an input or grid electrode 29, and an anode or plate electrode 30. A wire 31 connects the grid with the bridgedgrid inductance circuit.

The plate 30 is connected through a wire ,I 32

with an inductance 33 in the field of one side of the bridged inductance 20. The other end of the inductance 33 is connected to a wire 34, leading to the primary 35 of an aperiodic transformer. The other side of the primary 35 connects to the positive side of the plate current source 6. At 36 is a by-pass condenser. The secondary 37 of the aperiodic transformer leads to an audio amplifying channel. It is a peculiarity of the detector circuit that several stages of audiofrequency amplification with air core coupled transformers similar to that employed in the so-called superheterodyne circuit may be used.

When the inductances 8 and 20 are of such value as to be used together over a given band of wave lengths, the condensers 9 and 27 may be of the same value. According to the present invention these condensers are operated simultaneously. I have shown them as being connected by a common operating shaft 38 with an operating dial 39. The tuning of the circuit comprising the inductance 8 and the capacity 9 broadens as the frequency increases and sharpens as the frequency decreases, a phenomenon well known in ordinary tuned circuits and for which the socalled straight line frequency condenser is used to give partial correction. Just the reverse is true of the balanced grid circuit comprising the inductance 20 and the capacity 27. In this circuit, the tuning sharpens as the frequency increases and broadens as the frequencydecreases. The two condensers 9 and 27 are accordingly adjusted to resonance at approximately the midpoint in the wave length band covered by the inductance. Being set in resonance at this point, they are mechanically coupled together. Any broadening in the tuning of one circuit is thereby automatically compensated for by a sharpening in the tuning of the other circuit, so that the receiving circuit will tune with substantially uniform selectivity over the entire wave length band to which the circuit is responsive.

A loop aerial is not satisfactory under all conditions of operation, having reduced sensitivity in steel frame buildings and apartment houses. The present invention provides a way by means of which the loop aerial can be retainedand its sensitivity increased by the use of a counterpoise.

The tube 15 and its input circuit affords complete rectification. and impresses it on the succeeding amplifying train. Better signal quality is obtained through the elimination of the usual means for effecting rectification, i. e., the grid leak and grid condenser, or the application of the biasing voltage to the grid.

It will be understood that the drawing is merely illustrative of one embodiment of the invention, and that the invention may be otherwise embodied and the circuit modified in various ways known to those skilled in the art to secure the same results.

I claim:

1. In an apparatus for receiving radio signals, a circuit constituting a stage of tuned radiofrequency amplification succeeded by a detector having a balanced input circuit, the two being operatively coupled to respond over substantially the same wave band, the tuning of one of said circuits broadening as the frequency increases, the tuning of the other of said circuits sharpening as the .frequency increases, and a common operating member for tuning both circuits.

2. In aradio receiving circuit, a collector circuit comprising a neutralized stage of tuned radiofrequency amplification wherein the tuning broadens as the frequency increases, and sharpens as the frequency decreases. a detector circuit following the collector circuit and operatively coupled thereto, said detector circuit having a balanced grid input circuit, the tuning of said detector circuit sharpening as the fre- 5100 quency increases and broadening as the frequency decreases, adjustable means for tuning each of said circuits, and a device for operatively connecting said means for effecting simultaneous adjustment thereof- I 3. In a wireless receiving circuit, a collector circuit in which as the frequency therein increases its tuning broadens, and sharpens as the frequency decreases, a detector having a Wheatstone bridge input circuit in which as the frequency therein increases its tuning sharpens, and broadens as the frequency decreases, two variable condensers for tuning said collector and detector circuits respectively, the one for the detector being across saidbridge input circuit, and means for connecting the movable plates of said condensers to vary them in unison.

4. In a radio receiving circuit, an input circuit comprising a neutralizedstage of tuned radiofrequency amplification, a detector circuit following said input. circuit and operatively coupled thereto, said detector circuit including a three electrode tube having a grid, the tube having a bridge in the grid circuit provided with two inductance arms and two capacity arms with a variable condenser across said bridge, the plate of the tube having an inductance inductively disposed with reference to one of the inductance arms of the bridge, said bridge serving the function of a grid leak and grid condenser, said bridge serving to balance the tube against free self-oscillation. I

5. In a radio receiving circuit, an input circuit comprising a stage of tuned radiofrequency amplification wherein there is a variable tuning condenser and wherein the tuning sharpens as the frequency decreases, a detector circuit following the input circuit and operatively coupled thereto through a bridge having two inductance arms'and two capacity arm's, wherein there isa variable tuning condenser across the bridge and wherein the tuning broadens as the frequency decreases,

both of said circuits being adapted to respond ,Irequency amplification having; a variable condenser therein for tuning the same, a succeeding detector circuit comprising a three element vacuum tube, a four-sided bridge circuit having two capacities and two inductances and having a tuning condenser across the bridge connected to the grid elements of the detector tube, means for transferring amplified signal impulses from said stage of radiofrequency amplification to a point in the four-sided bridge circuit, and a common operating means for both tuning condensers.

7. In a radio receiving circuit, a stage of radiofrequency amplification having a variable condenser therein for tuning the same, a succeeding detector circuit comprising a three element vacuum tube, a four-sided bridge circuit having two capacities and two inductances and having a tuning condenser across the bridge connected to the grid elements of the detector tube, means for transferring amplified signal impulses from said stage of radiofrequency amplification to a point in the four-sided bridge circuit, and a common operating means for both tuning condensers, said bridge serving also to serve as a means for causing the tube to rectify whereby biasing voltages need not be impressed on the grid and whereby a grid means and grid condenser may be dispensed with, said detector having a plate circuit which includes a feed-back coupling to the bridge in the grid circuit of the detector.

8. In a radio receiving apparatus, a detector unit comprising a three element tube with a balancing bridge in the grid circuit, said balancing bridge having a tuning condenser connected across it, the balancing bridge with its tuning condenser constituting means for causing the tube to rectify in the absence of a grid bias or grid resistance and condenser.

9. In a radio receiving apparatus, a stage of tuned radiofrequency amplification having a variable condenser for tuning it, a detector unit.

succeeding the amplifying stage and comprising a three element tube with a balancing bridge in the grid circuit, said balancing bridge having a tuning condenser connected across it, the balancing bridge with its tuning condenser constituting means for causing the tube to rectify in the absence of a grid bias or grid resistance and condenser, the tuning condenser of the amplifying stage and tuning condenser in the bridge circuit being mechanically coupled to operate in unison.

10. A radio receiving circuit comprising a three-element detector tube having a cathode, a

grid and plate, a plate circuit including a source of direct current having the positive pole thereof connected with the plate and having the negative pole connected with the cathode, a circuit for the grid of said tube connected with the grid and with the cathode of the tube and having a low direct current resistance and a high alternating current impedance, and a second circuit between the grid and cathode having a low alternating current impedance and being open against the passage of direct currenttherethrough, said two circuits connecting with the grid through a bridge circuit of which they form. a part.

11. A radio receiving circuit comprising a detector tube having a cathode, agrid} and a plate, the plate circuit including a source of dilfQQlLCl11- rent having the positive side thereof connected with the plate and the negative side thereof con-.-

nected with the cathode, a grid circuit forthe detector tube comprising a low resistance direct current path from the grid to the cathode of the tube, whereby the grid is maintained at a negative potential with respect to the plate, and means in said grid circuit offering a high impedance to against the passage of direct current thererent path between the grid and the cathode, a

radiofrequency inductance in the grid circuit between the bridge and the cathode offering an impedance to alternating current impulses from the grid to the cathode, and a second connection leading from a point in the bridge circuit to the cathode and which is open against the passage of direct current therethrough but provides a low impedance to high frequency alternating current impulses, said connection being made with a third point on said bridge.

MAURICE M. PHILLIPS. 

